Synthesis of zinc titanates was carried out using a simple precipitation method followed by calcination at different temperatures to obtain different phases of the material. The phase transition characteristics, presence of functional groups, structural aspects and optical bandgaps with respect to calcination temperature were studied by thermal analysis, EDAX, FT-IR, powder XRD, Raman and UV-Vis spectroscopy respectively. The compound on heat treatment at 100 • C for 24 h showed broadened peaks in XRD. With increasing temperature of calcination, the compound appeared to turn to crystalline phase and cubic ZnTiO 3 phase was observed at 600 • C. Partial phase transformation of cubic phase ZnTiO 3 into hexagonal ilmenite type ZnTiO 3 was observed in the temperature range 700 • C to 900 • C. At 1000 • C both cubic and hexagonal ilmenite phases decomposed into cubic phase Zn 2 TiO 4 and rutile TiO 2. FT-IR showed M-O bonds in the range of 400 cm −1 to 700 cm −1. Raman spectra of cubic defect spinel ZnTiO 3 and cubic inverse spinel Zn 2 TiO 4 were found to be similar. The optical bandgap calculated using diffuse reflectance spectra was found to be in the range of 3.59 to 3.84 eV depending on calcination temperature.

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The freeze-drying method of metal oxides synthesis has a number of advantages such as high homogeneity, varying porous structures, morphologies and uniform particle size distribution, etc. Because of these advantages, the binary metal oxides ZnO, TiO2 and ternary metal oxide ZnTiO3 were synthesised by the freeze-drying method. The synthesised materials were characterised by X-ray diffraction (XRD), Fourier transform-infra red spectroscopy (FT-IR), UV-VIS spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The as-synthesised metal oxides were calcined at different temperatures to study the phase evolution and morphological changes. The crystalline cubic-phase ZnTiO3 (a = 8.3948Å) was obtained on calcination of the precursor at 600 • C, and decomposed to the cubic phase Zn2TiO4 (a = 8.4580Å) and rutile TiO2 (a = 4.5955Å and c = 2.9593Å) at 1000 • C. The band gap of ZnO (3.28-3.10 eV), TiO2 (3.37-2.97 eV) and ZnTiO3 (3.92-3.80 eV) calculated using Tauc's relation was found to vary inversely with calcination temperature and phase transition. Prasad et al. (2010) reported the synthesis of 100 % nanostructured rutile TiO 2 by a combined ultrasoundassisted sol-gel technique. The zinc titanate system is an interesting system, having different polymorphic phases such as cubic defect spinel Zn 2 Ti 3 O 8 , cubic inverse spinel ZnTiO 3 , hexagonal-ilmenite type ZnTiO 3

Structural and Optical Properties of Zinc Titanates Synthesized by PrecipitationMethod. -ZnTiO 3 is precipitated from an equimolar mixture of TiCl3 and ZnCl2 in 12% aq. HCl solution (pH 1.4) by addition of 1 M NaOH up to pH 7. The dark blue mixture of Zn(OH) 2 and Ti(OH)3+x is further oxidized by air to white ZnTi(OH)6 before being calcined (SiC oven, gradual heating between 100 and 1000 C, 2 h each). With increasing calcination temperature, the amorphous compound turns into crystalline cubic ZnTiO 3 (600 C). Partial phase transformation into hexagonal ilmenite-type ZnTiO3 is observed between 700 and 900 C. At 1000 C both cubic and hexagonal ilmenite phases decompose into cubic Zn 2TiO4 and rutile TiO2. Calculated optical bandgaps from diffuse reflectance spectra are in the range of 3.59 to 3.84 eV depending on the calcination temperature. -(BUDIGI, L.; NASINA*, M. R.; SHAIK, K.; AMARAVADI, S.; J. Chem. Sci. (Bangalore, India) 127 (2015) 3, 509-518, http://dx.doi.org/10.1007/s12039-015-0802-5 ; Mater. Phys. Div., VIT Univ., Vellore 632 014, Tamilnadu, India; Eng.) -J. Schramke 28-015